This invention relates to pressure transducers, and more particularly to pressure transducers having a flexible magnetically permeable diaphragm reactively coupled to stationary reactance elements, the degree of coupling being determined by the position of the diaphragm.
It is well known that numerous physical phenomena can be represented by sets of pressure differentials, changes in the value of a particular phenomenon being indicated by a change in the differential between either two variable pressures, or by a change in the differential between a variable and a reference pressure. In many cases the representative pressure differential varies non-linearly with changes in the particular phenomenon of interest, requiring a conversion from a pressure differential reading when a direct indication of the phenomenon is desired. For example, airspeed may be measured by a sensing device such as a Pitot tube arrangement which obtains a pressure differential between incoming and outgoing fluid streams. The resulting pressure differential, however, varies non-linearly with airspeed, necessitating the introduction of a compensating mechanism if a linearized airspeed output is desired. In the case of an altimeter, the change in the absolute pressure exerted by the ambient atmosphere as altitude above the surface of the earth increases is exponentially related to the altitude. The measurement of altitude therefore involves the measurement of the differential between a non-linearly related variable pressure and a reference pressure.
Many data dependent devices such as air data modules, computers, and flight control units require information on altitude, airspeed, or the like in linear form in order to provide "MACH Number" indications or to perform control functions. The thrust of much of the prior art, however, has been directed toward the development of sensor mechanisms having non-linearized outputs which track variations in the input pressures as directly as possible. For example, a number of variable reactance mechanisms have been designed in which a diaphragm is positioned equidistantly between a pair of inductance coils. When a representative pressure differential is applied across the diaphragm, small deflections of the diaphragm result which in turn change the magnetic coupling between the diaphragm and each of the coils, the net effect being an electrical output that varies substantially linearly with the input pressure differential. If a linear representation of the phenomenon of interest is ultimately desired, rather than the pressure differential itself, additional electronic equipment must be provided in order to modify the output signal, thereby increasing the cost of the transducer.
An additional limitation associated with the prior art is the frequent use of flat diaphragms and the attachment of same to the transducer housing by machining at the diaphragm edges. This method of support generally requires a thicker diaphragm for structural reasons than is necessary to satisfy the magnetic requirements of the transducer. Such diaphragms, typically about 2.5 mm in thickness, may exhibit less flexibility than could be achieved with a thinner material.